This paper,which compares geological background structure, earthquake sequence and various source parameters, comes to the following conclusions: 1) The 2014 M4.7 and M4.5 earthquakes are related to the northern section of the Xiannüshan fault microscopically and the nearest fault to the M4.3 and M4.1 earthquakes in 2017 is the Zhoujiashan-Niukou fault. 2) The M4.7 and M4.5 earthquakes in 2014 are rich in aftershocks with more than 500 aftershocks recorded. Among them, aftershocks of magnitude 2 and above are recorded 5 times with the maximum aftershock of M2.9 (ML3.5), with aftershocks lasting more than one month. The 2017 M4.3 and M4.1 earthquakes recorded only 160 aftershocks, including 3 aftershocks above level 2 and M2.6(ML3.3) with the largest aftershocks lasting about 20 days. 3) The best focal depth of the M4.7 and M4.5 earthquakes in 2014 is about 7 km. In 2017, the source depth of M4.3 and M4.1 is 3~5 km. 4) The dominant and corner frequencies of the main shocks in 2014 M4.7 and M4.5 earthquakes are not high; the dominant frequency is 1.5~8.0 Hz and the corner frequency is 3.0-8.0 Hz.Levels of the frequency spectrum of M4.3, M4.1 earthquakes in 2017 are mainly distributed at the dominant frequency and the corner frequency is low, suggesting fall or shallow landslide type characteristics.
GPS data from continuously operating stations both in Nepal and in the southern Qinghai-Tibet plateau are processed and three-dimensional transient postseismic displacements are calculated during the first year after the earthquake. Significant postseismic displacements concentrate in northern Nepal, especially along the national boundaries between Nepal and China. The amplitudes and azimuths of the horizontal postseismic motions exhibit a pattern similar to that of the coseismic offsets. Almost all stations in Nepal record postseismic uplift. Kinematic finite fault afterslip models are constrained using GPS measurements. The preferred afterslip model shows that the afterslip occurred in the down-dip portion of the coseismic rupture with an average slip-depth of 20 km. The maximum depth of the raw afterslip model extends to 30 km. However, subtle afterslip is detected in the shallow portion of the fault. The moment release is estimated to be 8.8×1019 Nm, equivalent to a magnitude of Mw7.3 and approximately 12% of coseismic moment. Then, the residual afterslip model is inverted by using the residual data set between the raw GPS data and viscoelastic models, which is based on lateral rheological structure. The residual afterslip model shows narrower and shallower afterslip located in the downdip of the rupture with an average slip-depth of 16 km. The moment released by the pure afterslip model decreases to 5.7 ×1019 Nm, corresponding to Mw7.2. The afterslip-coseismic moment ratio drops to 8%. Our simple multiple mechanism model not only improves the data fit but also makes the residual afterslip distribution more physically reasonable. Our afterslip models show no slip within the shallow unbroken portion of the fault in the postseismic period, implying it is accumulating elastic strain and will be released through earthquake in the future.
Concerned with truncation error in the earth gravity field model, we calculate the long wavelength high anomaly by the EGM2008 model, the residual terrain model (RTM) high anomaly by the DTM2006.0, the SRTM model and the residual high anomaly by GPS/leveling control points. The accuracy and computational efficiency of the RTM high anomaly model obtained by using different integral radius combination schemes is studied and compared. Finally, the CGGM2015 model and the GPS/leveling points are used to evaluate the geoid model’s accuracy and to verify the results.
Using mobile gravity measurements from 2010 to 2016 in northeast China, we systematically analyze regional gravity field changes and variation characteristics of gravity before and after the 2013 Qianguo MS5.8 earthquake swarm. The results show that the inter-annual and dynamic changes of gravity present NW and near NS direction in the study area, which differs from the structural framework of NE and NNE direction. This suggests that the variation of gravity field is weak in structure control. Generally, gravity changes are relatively gentle in northeast China, with rarely more than 60 μGal gravity gradient zone. This phenomenon shows that the level of underground structural activity and material migration is relatively stable in an indirect way. There are obvious gravity variation characteristics during the process of the earthquake preparation before the Qianguo MS5.8 earthquake swarm and the Tongliao MS5.3 earthquake. These cause continuous accumulation of seismic energy and the occurrence of earthquake rupture. The shock recovery adjustment of the gravity field after the earthquakes will take three or more years.
A new GLDAS_NOAH_M.2.1 land water model and its old version of GLDAS_NOAH_M.001 from January 2003 and June 2016, totally 162 months, are investigated here with GRACE satellite gravimetry observations to study soil moisture and total mass change in the Qinghai-Tibet plateau. Our result shows that GLDAS_NOAH_M.2.1 has an improved precision in simulating soil moisture change. Here, 6 study regions are divided and in each region these three data sets are used to estimate mass changes, whose correlation coefficient and periodic terms are derived. Compared with GLDAS_NOAH_M.001, GLDAS_NOAH_M.2.1 has a better performance in correlation with GRACE in terms of periodic variations. The correlation between GLDAS_NOAH_M.001 and GRACE is very poor in northern Tibet, while GLDAS_NOAH_M.2.1 has improved this condition. In terms of secular mass change, GLDAS_NOAH_M.2.1 brings a difference at the order of -6.4~4.5 Gt/a in different regions and a total different of -10.4 Gt/a in the main part of Qinghai-Tibet plateau.
The availability of the current GNSS RTK algorithm in the city environment is still low and can rarely meet centimeter level positioning accuracy of observation epochs, especially under dynamic conditions. This paper attempts to apply the partial ambiguity fixing algorithm to the city dynamic environment GNSS RTK positioning. This can speed up ambiguity search efficiency and increase the available high precision positioning of the number of epochs. The vehicle borne data in the urban environment is used to verify the availability of the partial ambiguity fixing algorithm.The test results prove that the algorithm can significantly improve the ambiguity fixing rate and increase the number of epochs of cm level positioning in urban environments.
Aiming at overcoming the difficulties of using TCAR method to fix ambiguity of Beidou triple-frequency long-baselines, we propose a sliding window method to fix the ambiguity of EWL, WL and NL. In long baselines, according to the experimental analysis of the relationship between window size and ambiguity successful rate, the ambiguity successful rate is mainly affected by ionospheric and tropospheric delays. Therefore, we use the sliding window method to fix EWL and WL ambiguities, the GIF-TCAR method to calculate NL ambiguity, at the same time using the sliding window method to fix NL ambiguity. The results indicate that this method can be used in BDS triple-frequency processing for real-time navigation and positioning.
GNSS triple-frequency is advantageous in reducing observation errors, so this paper advances a new algorithm of fast carrier phase observation accuracy estimation. Based on the assumption that GNSS triple-frequency carrier observations are independent, we use sliding polynomial fitting to get the observational precision of triple-frequency carrier GIF(Geometry-Free Ionosphere-Free) combinations. GPS and BDS triple-frequency experimental data results show that the algorithm can be used to quickly estimate the triple-frequency carrier phase observation precision, so it can provide a fast and accurate random function model for single precise point positioning.
The integrated BDS/GPS kinematic differential positioning algorithm is studied, and we analyze the benefit of the BDS signals on the ambiguity resolution. Experiments are conducted based on the kinematic measurements collected from the regions with serious signal occlusion. Test results show that BDS/GPS integration increases the number of the visible satellites, strengthens of the geometric structure and improves the success rate and reliability of ambiguity resolution. In addition, the positioning accuracy is 8 mm with the GPS/BDS integration in the horizontal direction, and 16 mm in the vertical direction. For GPS alone, the positioning accuracy is 3 cm and 8 cm, respectively.
The BDS satellites have yaw attitude maneuver periods and may run in the shadow. These states reduce the orbit determination precision of the dynamic model. In view of the above problem, we use the dynamic orbit determination method, in which pseudo-stochastic pulse parameters are estimated together, to calculate BDS satellite orbits. We analyze the impacts of the pseudo-stochastic pulse parameters estimation schemes on the different estimation intervals of parameters on the orbit determination precisions of BDS satellites’ different statuses, including normal status, yaw attitude maneuver status, and shadow running status. The results show that under the normal status, the precision of GEO satellite orbit determination is improved significantly by the pseudo-stochastic pulse parameters. The estimated interval of the pseudo-stochastic pulse parameters is in good agreement with all kinds of satellite operation periods. For the yaw attitude maneuver status and the shadow running status, the pseudo-stochastic pulse parameters, estimated every 6 hours, are helpful to improve the orbit determination precision of the corresponding satellites.
The RAIM(receiver autonomous integrity monitoring) availability effect in the Asian-Pacific region at non-precision approach(NPA) caused by each GEO satellite is counted using the RAIM availability adjustment method. Results show that the maximum availability differences affected by GEO satellites are 07∶00~08∶00 and 15∶00~16∶00, but the influence of each GEO is different. The orbit control periods of 14∶00~23∶00 for GEO C04 and 00∶00~05∶00 for GEO C05 make system availability lower than 99.9%, mainly caused by the designated position of the two GEO satellites and the regression cycle of MEO satellites. In addition, in order to reveal the availability improved by the new C13, which is an initial operational capability IGSO satellite, availability before and after having the BDS C13 satellite are obtained. It can be seen that the average RAIM availability reaches 99.99% after enabling the C13 satellite.
The influence of the subdaily signal represented by the multipath on the characteristics of the short baseline time series is evaluated in this paper. Results show that multipath will introduce spurious signals for a long period with amplitude 0.1~0.3 mm in the height direction, but little in the plane direction. Unmodeled elevation-dependent subdaily signals will introduce spurious long period signals to the daily coordinate time series in the direct component, but the spurious amplitude can be decreased by increasing the cutoff of elevation properly.
The meteorological parameters (air temperature and air pressure) estimated by GPT2 are analyzed and assessed using adjacent radio stations in the area of Shandong province. Further, GPT2 model is applied to SDCORS precipitable water vapor inversion. The research shows that the average deviation of air temperature and air pressure estimated by the GPT2 model are -1.61 ℃ and 0.53 Pa, the average standard deviation is 2.84 ℃ and 4.42 Pa, and the mean root mean square error is 3.27 ℃ and 4.49 Pa, respectively. Additionally, the mean deviation of SDCORS/PWV is 1.22 mm, the mean value is 3.05 mm, the mean square error is 3.46 mm, which is higher than that of GPT model, and the reliability is strong. For CORS stations without meteorological sensors, based on the GPT2 model to estimate the temperature and pressure, it is helpful to use the regional CORS to invert the precipitable water vapor, and to further effectively monitor and forecast the atmospheric precipitable water.
In a regional plane coordinate system, due to strong correlations between coordinate vectors in the coordinate systems, the matrix of normal equations creates severe ill-conditioning in the coordinate transformation, and leads to unreliable transformation parameters between the coordinate systems. The ill-conditioning of the transformation coefficient matrix is solved by introducing datum rotation center in the plane coordinate transformation model, and reliable coordinate transformation parameters are obtained. This method is validated with practical data.
For the shortcomings of shorter monitoring distance and low-level automation in vision measurement, we propose a deformation monitoring method based on shape matching, edge and region detection of the target. We design a monitoring mark suitable for the method, as well as corresponding algorithms. We choose SLR cameras to carry out experiments, and use continuous shooting smooth method and matching correction technology. We weaken measurement errors caused by environmental factors and reflector and shutter mechanical movement of camera. The visual deformation monitoring software is developed with VS2015 and QT programming platforms and C++ programming language. Long-term monitoring experiments are carried out. Our research is helpful for considering the feasibility, validity and monitoring precision of deformation monitoring method based on visual measurement.
